Changing detected display size in inches (not resolution)

I have two functionally identical Dell displays attached to my mini, but they show up as different sizes. How do I change the detected display size in inches? This is not about the apparent resolution, it's what MacOS thinks the physical display size is.

Mac Mini (2018), Mojave 10.14.6

HDMI port -> high quality HDMI cable -> Dell U2720Q

USB-C port -> Apple HDMI adapter -> high quality HDMI cable -> Dell U2720QM

When I go to About This Mac - Displays, it shows the U2720Q detected as "27-inch 3840 x 2160)", but shows the U2720QM as "61-inch (3840 x 2160)".

How do I tell the display manager that both monitors are physically the same size (both in real life, and in supported pixels)? Currently, I have to leave one at Default for Display, and then squish the scaling on the QM monitor so it's approximately the same size text, which really hurts my eyes.

Note: the Dell U2720Q is functionally the same exact monitor as U2720QM, the only difference is the model number denotes a direct Dell sale, versus a reseller sale. So I can't understand why they're reported as different physical sizes, unless the Apple HDMI adapter is... being stupid.

Any tips on 1) how/why the Q vs. QM monitor might possibly be different, or 2) how to go into the device driver and change it's bits to recognize that both monitors are really the same thing?

Thanks!